Employers' responsibilities would be limited to enrollment, processing payroll contributions and making modest employer contributions. Fiduciary responsibility for selecting money managers would be handled by an independent board of trustees.

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As with existing retirement savings, tax incentives would be offered for employers and employees to participate.

“This is not government spending. The essence of it is private investment,” Mr. Harkin said at a news briefing Friday. “It's sort of a middle ground between pensions and 401(k)s. Employers bear no investment risk; the risk is shared by all.”

Mr. Harkin is also proposing several substantial changes to Social Security benefit calculation methods, including increasing the amount of income to be replaced, changing the price index used to set COLAs, and raising more payroll taxes by phasing out the $110,000 income cap.

He said the changes, along with a new universal pension fund, are needed to close a $6.6 billion gap between what people have saved for retirement and what they need to retire on, as calculated by the Center for Retirement Research at Boston College.

A report issued Friday that detailed Mr. Harkin's proposals will be “the starting place in an evolving discussion about retirement security,“ he wrote in the introduction. He plans to spend the next few months working with business and labor leaders, policy experts, pension advocates and congressional colleagues on pension reform.

Before drafting specific legislation, Mr. Harkin said he hoped to spark discussion among interested parties. “We've got pretty good data and ideas about where we want to go. I'm under no illusions that we're going to get anything done this year, but I want to be ready to go in with this next year. “